The present invention relates generally to a method and structure of controlling an apparatus and, more particularly, to a method and structure of controlling a fuel injector via electronic trimming.
In an engine fuel system having a plurality of fuel injectors, it is typically desirable that each injector deliver approximately the same quantity of fuel in approximately the same timed relationship to the engine for proper operation. Several problems arise when the performance, or, more particularly, the timing (i.e., the time between the application of a fuel delivery command and the Start of Injection (SOI)) and delivery (i.e., the quantity and pressure of the delivered fuel) of the injectors diverge beyond acceptable limits. One problem caused by injector performance deviation or variability is that different torques are generated between cylinders due to unequal fuel amounts being injected, or from the relative timing of such fuel injection. Further, knowledge that such variations are inevitable require engine system designers to account for this variability; accordingly, many engine systems are designed not for peak or maximum cylinder pressures or output, but rather, are designed to provide an output equal to the maximum theoretical output less an amount due to the worst case fuel injector variability.
One approach for solving these problems in unit injectors is the so-called select fit manufacturing process. Generally, a common procedure involves flowing fluid through each unit injector nozzle and pumping mechanism and categorizing each nozzle and pumping mechanism accordingly. During assembly, nozzles are matched with pumping mechanisms knee to be compatible, depending on the category into which each was categorized. The disadvantage associated with this approach is the relatively high cost involved with sorting the nozzles and pumping mechanisms and maintaining these groupings for the duration of the manufacturing and assembly process,
Another approach for solving these problems involves extremely rigid manufacturing procedures for achieving high manufacturing precision necessary to meet the desired design specification. Such high manufacturing precision has the disadvantage of increasing the manufacturing cost, including the cost involved in manufacturing precision components and subassemblies and the costs related to the subsequent assembly process. Further, neither of the above-mentioned manufacturing-oriented solutions satisfactorily controls rejection of completely assembled injectors that fail to fall within the timing and delivery tolerances of the design specification. Thus, excess scrap remains a problem with these manufacturing-oriented approaches.
With the advent of increasingly sophisticated electronic control, a new approach to the problem of timing and delivery variations has emerged. In known electronic fuel injection systems, especially diesel-cycle internal combustion engine systems, the timing or start of injection, as well as the end of injection, or duration (delivery) is controlled by as electronic control, which controls these parameters for all of the engine cylinders.
An early attempt at using an electronic control to compensate for individual injector timing and delivery variations in an engine system involved measuring the flow characteristics of a particular injector at a single operating condition, and obtaining constants from this empirical testing, relative to an ideal fuel injector, and using these constants to modify a nominal control signal to compensate for the measured variation. This approach has proven unsatisfactory because it does not take into account the fact that timing and delivery variations exist not only between injectors, but as a function of the particular operating condition at which the injectors are operated. For example, it may be observed that at a low speed, low load condition, an individual injector may have greater variability from nominal specifications than at a high speed, high load condition. Thus, this approach has failed to provide a reduced injector to injector and injector to nominal performance variation necessary to meet today""s increasingly strict emission standards.
Others have tried to compensate for variation in the start of injection characteristic of individual injectors in an engine system by designating a proxy of the timing or the start of injection characteristic of the injector. In general, these methods first electrically detect the closure of a valve used in controlling the start and duration of fuel injection, in response to an injection command. These methods further assume that the time between valve closure and the start of injection is fixed. Given these two time intervals, the injection command can be modified to compensate for variation in the time between the injection command and valve closure. The problem that remains with this type of approach is that the detected valve closure does not precede the start of injection by a fixed time period. Many factors, including manufacturing and assembly variations, contribute to vary the actual start of injection from a nominal value. Thus, this approach does not eliminate injector to injector and injector to nominal variation due to variations of the valve-closure to start of injection time interval.
Accordingly, there is a need to provide an improved method and structure for controlling an apparatus, such as a fuel injector, that minimizes or eliminates one or more of the problems as set forth above.
This invention provides for reduced variation of a resultant characteristic of an apparatus with respect to a nominal resultant characteristic, and further with respect to a resultant characteristic of another apparatus, without the prohibitive expense and inherent limitations associated with prior art manufacturing electronic control approaches. In general, the method of this invention is performed in conjunction with an apparatus of the type having a nominal resultant characteristic at a plurality of operating conditions, and controllable in accordance with a control signal to achieve the nominal resultant characteristics. The method comprises three basic steps. The first step includes measuring the resultant characteristic associated with the apparatus at a plurality of operating conditions.
In the second step, a control signal is adjusted as a function of the resultant characteristics of the apparatus measured in the first step. Finally, in the third step, the apparatus is controlled in accordance with the adjusted signal such that the resultant characteristics of the apparatus, when operated, approach the nominal resultant characteristics expected of an apparatus of that type.
The method of the present invention is advantageously employed in the control of a plurality of fuel injectors of the type having a nominal start of injection characteristics, and where fuel injection is controlled by a fuel delivery signal. The method of the present invention, as applied to electronically-controlled fuel injectors, simply and inexpensively reduces the start of injection variation as between a plurality of fuel injectors, and with respect to a nominal start of injection characteristic of injectors of this type. The method comprises four basic steps. The first step includes measuring, for each injector, a respective start of injection characteristic. The next step comprises associating, for each injector, the measured start of injection characteristic with the respective injector. The third step includes adjusting the fuel delivery signal, for each injector, as a function of the variation of the measured start of injection characteristic from the nominal start of injection characteristic for injectors of that type. The fourth and final basic step of the method of this invention includes controlling each injector in accordance with a respective adjusted fuel delivery signal to reduce start of injection and variation.
A problem with prior art manufacturing-oriented approaches for reducing performance variations involved costly nozzle/pumping mechanism sorting and matching. Accordingly, in a further aspect of the present invention, the basic step of associating the measured start of injection characteristic with the respective injector includes the substep of categorizing each injector, based on a respective measured start of injection characteristic, into one of a plurality of trim categories. The trim category designation into which the injection has been categorized is then permanently recorded on the injector itself. The above-mentioned basic step of adjusting the fuel delivery signal accordingly further includes the substeps of reading the data (trim category designation) recorded on the injector and inputting this data into a control means, which is provided for generating the fuel delivery signal. These aspects of the present invention eliminate costly sorting, matching, and tracking the resulting assembly. One way in which the trim category designation is permanently recorded on each injector is through the use of a unique identifier such as a bar code. Accordingly, the steps of reading the data recorded on the injector and inputting this data into the control means are performed by the substeps of seeing the bar codes recorded on the injectors, interpreting each bar code to reconstruct the trim category designation, and transmitting the reconstructed trim category designation into the control means.
A further application to which the present invention may be advantageously employed, is the operation of a plurality of electronically-controlled fuel injectors of the type having a nominal delivery characteristic as a function of operating conditions, where each injector is controlled to deliver fuel by a fuel delivery signal. This method of the present invention comprises four basic steps. The first step includes measuring, for each injector, a respective delivery characteristic at a plurality of operating conditions. The next step of this method comprises associating, for each injector, the measured delivery characteristic with the injector so measured. In the third step, the fuel delivery signal for each injector is adjusted as a function of the variation of the associated measured delivery characteristic from the nominal delivery characteristic for the measured operating conditions. Finally, in the fourth basic step, each injector is controlled in accordance with the respective adjusted fuel delivery signal to minimize delivery variation. A significant aspect of the above-described method of the invention is the step of measuring a delivery characteristic at a plurality of operating conditions. The ability to xe2x80x9ctrimxe2x80x9d injector fuel delivery variations as a function of operating conditions permits a control system to optimize timing and delivery control to advantageously reduce emissions at all operating conditions, as well as increase performance beyond that achievable through prior art mechanically-trimmed methods.
In a further aspect of the present invention, a method is provided for accurately and inexpensively reducing start of injection and delivery variation of electronically-controlled fuel injectors of the type having a nominal start of injection and nominal delivery characteristics. This method of operating a plurality of fuel injectors comprises the steps of measuring, for each injector, a respective start of injection characteristic and delivery characteristic. Next, each injector is categorized into one of a plurality of trim categories as a function of the variation of the measured start of injection and delivery characteristics from the respective nominal start of injection and delivery characteristics for injectors of that type. Each trim category has associated therewith a start of injection offset value and a delivery offset value to be used in a later step for calculating a fuel delivery signal to control the fuel injector. The next step includes recording the category into which each injector was categorized on the respective injector. The fourth step includes storing the respective category recorded on each injector in a memory means of a control means. The control means generates the fuel delivery signal that controls the fuel injectors. The next step includes calculating the fuel delivery signal as a function of actual operating conditions based on nominal start of injection and delivery characteristics. In the next step, the fuel delivery signal for each injector is adjusted as a function of the respective start of injection and delivery offset values. Finally, each injector is controlled in accordance with a respective adjusted fuel delivery signal to reduce the start of injection and delivery variations from injector to injector, as well as from injector to nominal.
In a further aspect of the invention, the last-discussed method is further applied to a hydraulically-actuated electronically-controlled injector having a second signal, in addition to the fuel delivery signal, by which it may be controlled. This second signal is an actuating fluid pressure command signal. Accordingly, this method of the invention further comprises the step of adjusting the actuating fluid pressure command signal for each hydraulically-actuated injector as a function of the respective start of injection and delivery offset values.
Novel structure is used to implement the above described methods of this invention. Accordingly, in a further aspect of the present invention, a system for controlling the delivery of fuel through a plurality of fuel injectors to an engine is disclosed where each injector so controlled if of the type characterized by at least one observed performance parameter. The system comprises sensor means for detecting at least one, and preferably a plurality of, operating parameters and generating signals indicative of each parameter detected, control means for generating a base fuel delivery signal for each injector, memory means coupled to the control means for storing trim data signals for each injector, the trim data signals being derived from observed performance parameter values taken at a plurality of operating conditions, wherein the control means is provided in the system for trimming the base fuel delivery signal for each injector as a function of the trim data signals for reducing performance parameter variation as between the injectors controlled by the system, as well as variation relative to a nominal performance parameter value.
The present invention provides a structure and method of controlling the operation of an apparatus, such as, for example, a plurality of fuel injectors, to reduce fuel injection timing and delivery variation as required to meet emissions and performance goals by compensating for or xe2x80x9ctrimmingxe2x80x9d the fuel injection timing and delivery variations of each injector via an electronic control responsive to previously measured resultant or performance characteristics of each fuel injector so controlled by the structure or method herein described.